Antibiotic Use

How do we go about selecting an antibiotic?

• Consider spectrum of activity (Image)

• Pharmacokinetics- How an organism affects a drug

  • Does it get to where we need it?

  • How is it excreted?

  • How is it metabolised?

  • What is the pH?

• Pharmacodynamics- How a drug affects an organism

  • The mechanism of action can be really important when making clinical choices

• Mechanism of Action = bacteria involved + bacteria location

  • Bacteriostatic (stops bacteria from growing) May be preferable in situations where killing bacteria can cause harm such as endotoxic shock

  • Bactericidal (actively kills the bacteria) Advantageous in animals which are immunosuppressed or neonatal animals

  • • In many situations either is fine

    • This can sometimes be affected by dose

• Licensing and Withdrawals

  • Check your data sheets!

  • Are there products licensed for this use in this species?

  • These are food producing animals

    • withdrawal periods are critical

  • If there is no licensed product we have access to the cascade

• Practicalities

  • Route of administration

  • Duration of Action

  • Volume of administration

  • Cost

• Responsible use of antibiotics

• Length and Course - long acting or daily

• Withdrawal Periods

What is the drug “cascade”?

• The cascade is a mechanism for vets to use when a suitable licensed product is not available

• Use of the cascade is justified when there is a risk to animal welfare

• Cost is not a justification for cascade use

• Any time we are using an unlicensed product OR using a product in a way in which it is not specifically licenced we are using the cascade and we must be able to justify it

If there is no licensed product for the desired condition, we can follow what four steps?

What are the additional requirements in using drugs for food producing animals?

• Must have known maximum residue limits (MRL - allowed annexes)

• Must be licensed for food producing animals in country of origin

• Apply minimum withdrawal periods

• 1.5 times the longest withdrawal period listed on the datasheet for any species

• 1 day if the longest withdrawal period listed is 0 days

• If no withdrawal is listed then eggs: 14 days, milk: 7 days, meat: 28 days

• Keep specific Records for 3 years

• Single holding (CPH) only

What does responsible use of antibiotics involve?

• Every time we use antibiotics we select for resistant bacteria

• The most responsible use is not to use them at all

• When we need to use antibiotics, we use them properly

• We protect the most critically important classes

What is the RUMA categorization?

Responsible Use of Medicines in Animals - Driving change to reduce Abs use in general, and focusing on reducing use of critically important Abs

• Category A - Avoid

• Category B - Restrict

• Category C- Caution

• Category D - Prudence

Describe main features of the Beta Lactams.

Beta Lactams

• Penicillin

• Amoxycillin

• Potentiated Amoxicillin (With clavulonic acid - which works against Beta lactamase)

• 1st and 2nd generation cephalosporins

• 3rd and 4th generation cephalosporins

Characteristics:

• Bactericidal

• Act by breaking down bacterial cell walls

• Excreted via kidneys and urinary tract

• Versatile and widely used

• 3rd and 4th generation cephalosporins are HPCIA

Spectrum of Activity: Image

• **Mycoplasma - no cell wall, beta lactams not effective

• Image

What is Beta lactamase?

• Defines the spectrum of activity for gram positive bacteria

• Some bacteria produce an enzyme called beta lactamase which is able to break down many of the Beta lactams (The Abs)

• These bacteria would therefore be resistant to those classes of Beta lactam

Describe main features of the Tetracyclines.

Tetracyclines

• Inhibit bacterial protein synthesis

• Bacteriostatic

• Broad spectrum

• Variable activity against mycoplasma

• Concentrate well in areas of inflammation due to their pH

• Antagonistic to Beta lactams

Spectrum of Activity

• **Circle = commonly used in large animal medicine

• Image

Describe main features of the Aminoglycosides.

Aminoglycosides

• Inhibit protein synthesis

• Bactericidal

• Gram negative spectrum of activity

• Often used in combination with penicillin

• Streptomycin is very effective agains A. lignieresii (wooden tongue)

Spectrum of Activity

• **Circle = commonly used in large animal medicine

• Image

Describe main features of the Sulphonamides (TMPS).

Sulphonamides

• Inhibit bacterial folate synthesis

• Broad spectrum

• Bacteriostatic (may be cidal in some instances)

• Good gut penetration

• Some protozoal activity

• Inhibited by pus

Spectrum of Activity

• Image

Describe main features of the Phenicols (Florfenicol used in farm med).

Phenicols

• Disrupts bacterial protein synthesis

• Bacteriostatic (can be cidal at higher doses)

• Broad spectrum

• Some products have a mycoplasma licens.

• Very good tissue penetration - penetrates joints, testicles, lungs and crosses blood brain barrier

• Commonly used for pneumonia and joint ill

Spectrum of Activity

• Image

Describe main features of the Macrolides.

Macrolides

• Inhibit bacterial protein synthesis

• Bacteriostatic

• Gram +ve and fastidious Gram -ve

• Good choice for mycoplasma

• Enter macrophages so concentrate well in areas of inflammation

• Often long duration of action

• Commonly used for pneumonia and lameness

Spectrum of Activity

• Image

Describe main features of the Lincosamides.

Lincosamides

• Inhibit bacterial protein synthesis

• Have a similar mechanism of action to macrolides

• Bacteriostatic at therapeutic concentrations

• Mainly gram positive spectrum of activity

• Good activity against anaerobic bacteria

Spectrum of Activity

• Image

Describe the main features of the Fluroquinolones.

Fluroquinolones

• Inhibit bacterial DNA synthesis

• Bactericidal

• Broad spectrum including mycoplasma

• HP CIA - avoid wherever possible

Spectrum of Activity

• Image

Summarize the criteria for antibiotic selection?

• Bacteria involved

• Bacteria location

• Bacteristatic or Bactericidal

• Licensing

• Responsible use of antibiotics

• Route of administration

• Length of course - long acting or daily?

• Withdrawal Periods

Summarize bactericidal vs. bacteriostatic.

Summarize - spectrum of activity for antibiotics.